Activity dynamics of amygdala GABAergic neurons during cataplexy of narcolepsy.

Recent studies showed activation of the GABAergic neurons in the central nucleus of the amygdala (CeA) triggered cataplexy of sleep disorder narcolepsy. However, there is still no direct evidence on CeA GABAergic neurons' real-time dynamic during cataplexy. We used a deep brain calcium imaging tool to image the intrinsic calcium transient as a marker of neuronal activity changes in the narcoleptic VGAT-Cre mice by expressing the calcium sensor GCaMP6 into genetically defined CeA GABAergic neurons. Two distinct GABAergic neuronal groups involved in cataplexy were identified: spontaneous cataplexy-ON and predator odor-induced cataplexy-ON neurons. Majority in the latter group were inactive during regular sleep/wake cycles but were specifically activated by predator odor and continued their intense activities into succeeding cataplexy bouts. Furthermore, we found that CeA GABAergic neurons became highly synchronized during predator odor-induced cataplexy. We suggest that the abnormal activation and synchronization of CeA GABAergic neurons may trigger emotion-induced cataplexy.

Amygdala GABA Neurons Project To vlPAG And mPFC.

The amygdala regulates multiple behaviors and emotions by projecting to multiple brain regions. However, the topographical distribution of amygdala neurons projecting to specific brain areas is still unclear. In the present study, we focus on determining whether single amygdala neurons project to the brain stem ventrolateral periaqueductal grey (vlPAG) and to the medial prefrontal cortex (mPFC). The mPFC neurons are involved in detecting emotional content while the vlPAG neurons are involved in regulating muscle tone. In VGAT-Cre mice a cre-inducible retrograde AAV tracer expressing tdTomato was microinjected into the ventrolateral periaqueductal grey matter (vlPAG), while a second retrograde AAV tracer with generic expression of GFP was delivered into the medial prefrontal cortex (mPFC). The results identified a subgroup of bifurcating GABAergic neurons in the central nucleus (CeA) and basolateral amygdala (BLA) that projects to vlPAG and mPFC. Based on these projections we suggest that amygdala GABA neurons may be involved in triggering emotionally-induced cataplexy in the sleep disorder, narcolepsy.

VGAT and VGLUT2 expression in MCH and orexin neurons in double transgenic reporter mice.

The neuropeptides orexin and melanin-concentrating hormone (MCH), as well as the neurotransmitters GABA (γ-Aminobutyric acid) and glutamate are chief modulators of the sleep-wake states in the posterior hypothalamus. To investigate co-expression of vesicular GABA transporter (VGAT, a marker of GABA neurons) and the vesicular glutamate transporter-2 (VGLUT2, a marker of glutamate neurons) in orexin and MCH neurons, we generated two transgenic mouse lines. One line selectively expressed the reporter gene EYFP in VGAT+ neurons, whereas the other line expressed reporter gene tdTomato in VGLUT2+ neurons. Co-localization between these genetic reporters and orexin or MCH immunofluorescent tags was determined using 3D computer reconstructions of Z stacks that were acquired using a multiphoton laser confocal microscope. Our results demonstrated that MCH neurons expressed neither VGAT nor VGLUT2, suggesting MCH neurons are a separate cluster of cells from VGAT+ GABAergic neurons and VGLUT2+ glutamatergic neurons. Moreover, most orexin neurons expressed VGLUT2, indicating these neurons are glutamatergic. Our data suggested that in the posterior hypothalamus there are four major distinct groups of neurons: VGAT+, orexin+/VGLUT2+, orexin-/VGLUT2+, and MCH neurons. This study facilitated our understanding of the role of these neurotransmitters and neuropeptides in relation to sleep/wake regulation.